The subject of this invention is a dental abutment, and a method for preparing a custom abutment for use in association with the fabrication of a custom dental prosthesis.
Dental prostheses which are rigidly attached to a patient's jaw using an attaching system consisting of dental implants and abutments are a popular alternative to removable dentures and removable partial dentures. Typical fixed dental prostheses use an implant which is bonded directly to the jaw of the patient, and an abutment which is attached to the implant for uniting the dental prosthesis with the implant. Most implant systems use a two-stage implantation procedure. In the first stage, an implant is installed in the jaw bone of a patient and the site is allowed to heal for a period of three to four months or more. After the implant site has healed and the bone has bonded to the implant, the second stage of the procedure begins. The top of the implant is exposed to view and an abutment is attached to the implant. An impression of the patient's mouth is made and the abutment is allowed to remain in the patient's mouth. An analog of the abutment is inserted into the impression which accurately replicates the abutment. Dental stone (plaster) is poured into the impression and when later separated from the impression, a cast of the patient's mouth is generated with the analog in the position of the abutment in the mouth. The framework for the dental prosthesis is formed around this abutment analog in the dental laboratory using wax or plastic to allow casting of the framework into a dental alloy. The prosthesis will finally be attached to the abutment in the patient's mouth.
A major problem with the dental implant abutment system is that abutments often cannot be oriented to adapt to the installation configurations necessitated by the structure of a patient's mouth. Dental implants are embedded surgically in the jaw bone of the patient. This means that the implant may be angled inwardly or outwardly from the jaw bone depending upon a patient's jaw bone configuration. The problem can be compounded by surgical error. This can be problematical, especially when the implant is embedded in the anterior (front) portion of a patient's mouth in which case the implant often is at a severe outward angle. This angular problem is created because of the length of the abutment protruding beyond the intended tooth contours, or because a retaining screw for the abutment would be visible on the front of the tooth, or because of the creation of problems in permitting a path of insertion of the prosthesis; that is, a misaligned implant is often divergent from other implants or supporting teeth in the mouth making the insertion of the prosthesis impossible.
This problem has been partially solved by offering abutments in pre-manufactured lengths and having pre-manufactured angles. However, such pre-manufactured abutments are not able to be adapted to all patients in all cases. The result of this is that some patients are not presently amenable to the installation of permanent dental prostheses using pre-manufactured abutments.
Presently, abutments are made of titanium, or of a combustible plastic to be cast into a dental alloy. Titanium abutments typically cannot be custom modified by a dentist or technician using available tools. The problem has been addressed by offering titanium abutments in varying lengths and with pre-manufactured angles. Although a titanium post abutment can be slightly reshaped or shortened, one cannot cast additional metal to a titanium post because the outside surface of titanium forms an oxide layer which inhibits any type of molecular bonding between the titanium and the dental alloy. Therefore, such a casted custom modified titanium abutment is prone to breakdown.
Plastic abutments to be cast into dental alloy cannot be fabricated with the accuracy of a machined metal abutment. The threads cannot be machined as accurately and also the resultant interface between the implant and cast abutment is not as accurate. This can produce an abutment with compromised stability. It is possible to add wax and cast to the plastic abutments in the dental laboratory; however, because the threads are plastic and compressible, the rotational position in the cast may be different in the laboratory than in the mouth. Also, because of the difficulties in casting threads accurately, the rotational position prior to casting plastic is usually different than after casting. This can often produce an abutment which appears correctly aligned in the laboratory but is severely misplaced in the mouth.
Therefore, titanium abutments, while being highly machined and capable of being accurately positioned in the patient's mouth, are not amenable to custom modification due the inability of the titanium to chemically or molecularly bond to any alloy that might be used to modify or "cast to" the abutment. On the other hand, plastic abutments, while being capable of some custom modification to conform the abutment to the patient's mouth, are not easily repositioned in the patient's mouth after casting due to the inaccuracy in casting plastic threads. As a result, some patients cannot be fitted with permanent dental prostheses.